Electronic Assembly Group and Method for Producing the Same

ABSTRACT

An electronic assembly group comprising a printed circuit board structure in a multilayer configuration that has at least two electrically conductive layers. The electronic assembly group also comprises an additional passive component that is connected to the two electrically conductive layers, each of which has at least one segment that extends beyond the multilayer structure to form connection regions, the passive component making contact directly at the connection regions.

RELATED APPLICATIONS

This is a continuation of International PCT Application No.PCT/EP2012/002622, filed on Jun. 21, 2012, which claims priority fromGerman application No. 10 2011 105 346.1, filed on Jun. 21, 2011, all ofwhich are hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to an electronic assembly group and amethod for its production, as well as an electric motor, for example foruse in a motor vehicle.

BACKGROUND OF THE INVENTION

Electronic components, or electronic units or assemblies for powerelectronics, are known, for example, in the form of DCB (Direct CopperBonding) modules. This usually means ceramic substrate with solderedpower semiconductors, onto which further necessary (passive) componentparts are connected. In the case of inverters/rectifiers these componentparts can be capacitors, particularly film capacitors and inductors.

Based on the above, an electronic assembly group and a method forproducing the same, as well as an arrangement of a multilayer printedcircuit board structure with an integrated power semiconductor and anadditional passive component part and an electric motor are proposedaccording to the invention.

SUMMARY OF THE INVENTION

The electronic assembly group according to the invention comprises aprinted circuit board structure with a multilayer structure ormultilayer configuration. The multilayer structure contains, in aconventional manner, at least two electrically conductive layers. Theinvention proposes to lengthen each of these two layers in such a waythat they exhibit a section projecting beyond the multilayer structure,said section defining a connection region for direct contact formed byan additional passive component part. These connection regions can bedesigned, for example, in a lattice-like or striped form.

This allows a significant reduction of the strongly present parasiticinductions in the known DCB modules with their long lines andconnections. Additionally, a short and low-inductive connection of powersemiconductors in the multilayer structure and a compact design is madepossible. The number of connection points between the active and thepassive component parts, particularly by bonding, is reduced, since onlythe connection region projecting from the printed circuit board coreremains to be connected with the passive component part. The additionalpassive component part, for example, can be a capacitor and/or aninductor and/or a resistor.

For the production of an electronic assembly group according to theinvention, a multilayer structure with an electrically conductivecarrier layer and at least one further electrically conductive layer areprovided. The carrier layer and the further electrically conductivelayer have layer sections projecting beyond the core region of themultilayer structures. Any layer sections not needed as connectionregions are at least partially removed, and also the prepreg layersections projecting beyond the core region are at least partiallyremoved. If necessary, remaining layer sections that project beyond thecore region are bent to create connection regions for a passivecomponent part. This provides a particularly simple production of acompact assembly with integrated connection regions that project beyondthe actual layer structure for a direct low-inductive connection of apassive component part without additional intermediary.

According to one variant, before the steps of the partial removal, atleast one through-connection between a projecting layer section of thefurther electrically conductive layer and a projecting layer section ofthe carrier layer is established, and the projecting layer section ofthe further electrically conductive layer is separated from the furtherelectrically conductive layer. This achieves the result that bothconnection regions projecting beyond the multilayer structure lie on thesame plane and have the same thickness.

By combining the connection regions projecting beyond the multilayerstructure with inductive component parts, such as, for example, ferritecores, targeted inductors with specific values can additionally becreated. These inductive component parts can be used alone or also incombination with other passive component parts such as a capacitor.

The connection regions can exhibit at least one recess, with a contactpad contained within it, for contact with a passive component part. Thissimplifies the direct connection with the passive component part. Thecontact pad, for example, can be electrically connected to theconnection region via at least one holding web or holding bar. Due tothis, during soldering/welding lower heat dissipation occurs because ofthe reduced cross-section of the holding web. The contact pads can thus,for example, be soldered directly to the Schoop layer of a filmcapacitor. Different geometries are possible for the arrangement of thecontact pads and also the holding webs. The holding webs can be arrangedin such a way that they take on different expansion coefficients or therelated mechanical tensions during use. The holding webs can, forexample, be arranged in a meandering or zig-zag way, or can allowdeformation or twisting due to their mounting geometries.

Further advantages and embodiments of the invention are apparent fromthe description and the attached drawing.

It is obvious that the aforementioned features, and those which arestill to be mentioned below, may be used not only in the respectivelystated combination, but also in other combinations or also bythemselves, without exceeding the scope of the present invention.

The invention is represented for illustrative purposes by means ofexemplary embodiments depicted via schematic drawings (not to scale),and is described in detail in the following, with references to theillustration in question.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a side view cutaway diagram through a first exemplaryembodiment of an electronic assembly group of the invention.

FIG. 2 shows a side view cutaway diagram through a second exemplaryembodiment of an electronic assembly group of the invention.

FIGS. 3 through 6 illustrate the production of the connection regionsaccording to the invention.

FIG. 7 shows a multilayer structure with separation layers for use inthe production of connection regions according to the invention.

FIGS. 8 through 12 illustrate an alternative production of theconnection regions according to the invention.

FIG. 13 shows a top view of an arrangement of a connection regionaccording to the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an electronic assembly group 50 according to the inventionin a side view cutaway diagram.

Assembly 50 contains a multilayer printed circuit board structure thathas a carrier layer 12 which carries an (embedded) semiconductorcomponent part 18. Extending above the carrier layer 12 and thesemiconductor component part 18 is a prepreg layer or one resin layer 20from an earlier prepreg layer above which lies a further electricallyconductive layer 14. It has a through-connection to the semiconductorcomponent part 18. On the top layer 14 a logic circuit 40 can beattached as shown, for example by lamination. According to the exemplaryembodiment shown, an electronic assembly group is a appropriate logiccontrol. However, the logic circuit pictured can also be a separatecircuit, and be coupled with conventional connection technology to thepower electronic part.

Beneath the carrier layer a second further electrically conductive layer16 is provided—separated by a second prepreg layer 22. It is arrangedsuch as to be electrically insulated from layer 12, but its materialthickness and its material properties are selected in such a way thatgood thermal conductivity and simultaneously high dielectric strength isachieved. The arrangement is positioned with the second further layer 16at a heat sink 60.

The connection with the heat sink 60 can be made directly in thefactory, so that the assembly according to the invention is deliveredalready complete with a cooling element. This would be an option, forexample, in the compact design shown in FIG. with a ring capacitorsurrounding the multilayer structure including the heat sink. On theother hand, the assembly can also be connected only at the destinationwith the element serving as a heat sink possibly already present there.The underside or bottom side of the assembly (i.e., the underside of thesecond conductive layer 16) can have an adhesive paste layer or similar(not shown), with sufficient thermal conductivity (cf. the example of amotor vehicle electric motor in Paragraph described below).

The carrier layer 12 is extended beyond the original multilayerstructure—to the right in the depiction of FIG. 1—and forms a connectionregion 12.2. In an analogous manner the further conductive layer 14 isextended in the opposite direction beyond the “core region” or“functional region” of the multilayer structure, to form a connectionregion 14.1. In the illustrated exemplary embodiment, the connectionregions 12.2 and 14.1 are connections for a capacitor C, which are thusdirectly connected to the drain and source connections of the powersemiconductor.

In this manner according to the invention, connection regions 12.2, 14.1are directly led out of the multilayer printed circuit board structureand are directly connected with a passive component part, i.e. in thepresent example a capacitor. Thereby a short connection from the passivecomponent part to the semiconductor component part 18 is achieved. Theelectronic assembly group according to the invention is of simpleconstruction and has a significantly raised assembly density/integrationas well as reduced parasitic inductions.

In addition, the connection regions 14.1 and 12.2 are executed as a loadinductor L. The load inductor L can be formed, for example, by one ormore ferrite cores.

The design according to the invention additionally permits directcontact of at least one of the load inductor-forming ferrite cores withthe heat sink 60.

FIG. 2 shows an alternative design of the electronic assembly group 50of the invention, having a ring-shaped capacitor C that is arrangedsurrounding the printed circuit board structure. The drain/sourceconnection regions 12.1, 14.1, 12.2, 14.2 in this case emerge on bothsides of the structure from the carrier layer 12 and the furtherelectrically conductive layer 14 so that altogether four connectionregions 12.1, 14.1, 12.2, 14.2 are present. Basically, the ringcapacitor can be connected with only two connections (as in theexemplary embodiment in FIG. 1); with four connections, however, theparasitic inductions that occur in the Schoop layer of the ringcapacitor would be reduced by half.

As is evident from the illustration of FIG. 2, by using a ring capacitorthe invention allows an especially compact and flat design, since theentire internal structure including the heat sink 60 is surrounded bythe capacitor. In an arrangement of this sort, the connection regionsaccording to the invention can be relatively short. The ring capacitorreceives within its inside (i.e. the opening of the ring) the multilayerprinted circuit board structure from which the connection regionsextend. The connection regions are directly connected to the connectionsof the ring capacitor. In the illustrated exemplary embodiment the heatsink 60 is also arranged inside the ring capacitor, in order to achievethe most compact design.

Of course, this can also be achieved with a rectangular capacitor.Alternatively, two separated capacitor packs can be placed left andright on the connection pairs 12.1, 14.1 and 12.2, 14.2.

In a specific application, the electronic assembly group can be arectifier/converter in an electric motor for an automobile. In thiscase, the assembly group can be placed in a particularly space-savingmanner directly (with a suitable thermally conductive connective layer(e.g. adhesive pastes, sinter pastes, soldering pastes, etc.) in-betweento prevent air gaps) on a cooling section (already present) of theelectric motor, such that this forms the heat sink 60, and no separateheat sink is necessary.

In order to produce an electronic assembly group according to theinvention, a standard multilayer structure 10′ is provided (cf. FIG. 3).This multilayer structure may be, e.g., a structure such as that knownfrom the parallel German patent application 10 2010 060 855.6 of thesame applicant.

The multilayer structure 10′ provided comprises a first conductive layer12, representing a carrier layer for a semiconductor component 18 (notdepicted). The multilayer structure 10′ also comprises a furtherelectrically conductive layer 14 which is located above the firstconductive layer 12 in the depiction of FIG. 3. A prepreg layer 20 whichmay consist of thermally conductive material is provided between the twolayers 12, 14.

The multilayer structure 10′ further comprises a second electricallyconductive layer 16 which is located underneath the first conductivelayer 12 in the depiction of FIG. 3 and separated from it by a secondprepreg layer 22. This prepreg layer 22 may also consist of thermallyconductive material.

The further electrically conductive layers 14, 16 may be copper foils,which can additionally be plated.

The multilayer printed circuit board structure of the invention may havea symmetrical structure around the carrier layer 12, i.e. the prepreglayers 20, 22 have the same thickness, just as the further conductivelayers 14, 16 are each of the same thickness. The symmetry of thestructure results in a high level of reliability of the assembly. Whileasymmetrical structures such as DCB substrates tend to bend whensubjected to the strain of temperature changes, this behavior isinhibited with the symmetrical structure described here.

The actual size/width of the electronic assembly group to be produced isindicated in FIG. 3 by the two dashed vertical lines, and is hereinaftertermed the “core region” or functional region K. In order to produce thelayer sections extending beyond the multilayer structure according tothe invention, the layers of the multilayer structure 10′ extend in thisprocess stage as far beyond the dashed lines on both sides ascorresponds to the desired length of the eventual/future connectionregions. These sections of the layers are designated by the addition of“0.1” or “0.2” to the reference signs. To the left and right (in therepresentation of the figures) of the carrier layer 12 or 12.2,respectively, are internal layers F which have been exposed by milling.

In the regions to the left and right of the dashed lines, the prepreglayers 20.1, 20.2, 22.1, and 22.2 may consist of the same (thermallyconducting) material as in the “core region” K between the dashed lines,or if indicated by cost considerations—of a cheaper standard material.That section of the multilayer printed circuit board structurecontaining the power electronic and, if applicable, control function isdesignated as core region K or functional region. The sectionsprojecting beyond this core region serve to realize the idea or gist ofthe invention, namely to create the possibility of a direct connectionfor passive components.

FIG. 4 depicts the multilayer structure after an etching process: thesections 16.1 and 16.2 of the second further electrically conductivelayer 16 extending beyond the core region have been etched away, as hasone of the two projecting sections 14.2 of the first furtherelectrically conductive layer 14. The prepreg layers are unaffected bythe etching step, as are the projecting sections 14.1 and 12.2 (whichwill still be needed later) of the first further layer 14 and carrierlayer 12.

In a further step, the exposed prepreg layers 20.1, 20.2, 22.1 and 22.2are substantially removed through milling (depth milling) (cf. FIG. 5),leaving a multilayer structure 10 the layers of which correspond in the“core region” to the desired dimensions, with two of the layers eachhaving one layer section 14.1, 12.2 projecting beyond the multilayerstructure 10. These layer sections 14.1, 12.2 are defined as connectionregions, and are bent as necessary in a subsequent process step suchthat they serve to directly contact a passive component (cf. FIG. 6).The connection regions may be formed as tabs or strips according to theinvention. In particular, the connection regions are so formed as to besuited for directly contacting at least one further passive componentwithout the need for additional connecting means (such as, inparticular, cables, etc.).

The connection regions 14.1, 12.2 so formed can then be connected to apassive components, in the present exemplary embodiment a condenser C,C′, e.g. by soldering, if necessary via a Schoop layer.

In addition, one or both of the connection regions 14.1, 12.2 can beformed as at least one load inductor L, in that the conductiveconnection region is enclosed e.g. in ferrite cores. The structure canalso be connected to a heat sink 60. The final product may be potted(casting 70; cf. FIG. 1).

One variant of the initial multilayer structure 10″ is shown in FIG. 7.The basic structure of the multilayer structure corresponds with thedepiction of FIG. 3, with the difference that separating foils 11, 13,15 are provided between the projecting layer sections 14.1 and 12.1 andtheir adjacent prepreg layer sections 20.1, 20.2, 22.2, said foilspermitting or easing the separation by mechanical means (throughpulling, peeling, etc.) of the prepreg layer sections 20.1, 20.2, 22.2from the eventual/future connection regions 14.1, 12.2. To this end, thecontour of the region to be removed is depth milled in order to provideaccess to the separating foil. The advantage is that only the contour,and not the entire surface, need by milled, etched or lasered. Insteadof the separating foil described and depicted (which may be, e.g., ateflon or teflon-like film), any other separating means may be used thatprevents the prepreg layer from sticking to the electrically conductinglayer. This separating means can also be a suitable liquid or paste-likematerial applied via screen printing, spraying, or immersion.

A further variant, as illustrated in FIG. 8, provides for what is called“plane offsetting”.

In this variant of embodiment, a multilayer structure 10′″ is providedin which the carrier layer 12 extends only slightly beyond the “coreregion” (reference sign 12′). The further electrically conductive layer14 is—as in the previous exemplary embodiments—extended on both sidesbeyond the core region (reference signs 14.1 and 14.2).

In a next step, a through-connection 17 (which may consist of severalthrough-connections, e.g. in the form of one or more rows ofthrough-connections) is made from the extended layer section 14.1 of thefirst further electrically conductive layer 14 to the short projection12′ of the carrier layer 12 positioned beneath it (cf. FIG. 9), followedby a separation of the layer section 14.1 from the first furtherelectrically conductive layer 14 at the boundary of the “core region”and before the through-connection 17 (cf. FIG. 10, reference sign 19).In this way, a contact is established between the (somewhat thicker)carrier layer 12 and the (thinner) connection region 14.1 of the furtherelectrically conductive layer 14, so that the carrier layer 12 has athinner “auxiliary” connection region. The effect is that the connectionregions both i) are on the same level and ii) have the same thickness.

Subsequently, depth millings are carried out from the side opposite thefirst further electrically conductive layer 14, i.e. from the side ofthe second electrically conductive layer 16, in order to create abending region 24 on either side of the core region. These depthmillings are carried out outside the core region, but close to it, sothat the connection regions can be bent as close to the core region aspossible. The depth millings go through all layers except the connectionregions 14.1 and 14.2 (cf. FIG. 11).

Finally, two depth millings may be carried out, also from the sideopposite the first further electrically conductive layer 14, i.e. fromthe side of the second electrically conductive layer 16. These seconddepth millings serve to create solder connections 26 in order to make itpossible to connect the passive component (cf. FIG. 12). The remainingregions 28 with sequences of layers below the connection regions 14.1and 14.2 can serve during potting as spacers between a housingsurrounding the electronic assembly group (not shown).

FIG. 13 shows an extract of a plan view of an embodiment of a connectionregion 12.2 or 14.1 according to the invention. The connection regionhas one or (as depicted) multiple recesses 30 (the embodiment of FIG. 13has four such recesses). Each recess 30 is provided with a contact pad32 which is provided and formed for welding or soldering to a contact ofthe passive component to be connected. In the embodiment shown, thecontact pad 32 has an essentially quadratic outline/footprint, though itmay take any other suitable form.

The contact pad 32 is connected electrically to the connection region bymeans of at least one holding web/bar 34. In the embodiment shown, fourholding webs 34 are provided for each contact pad 32; however, more orfewer may be used. The holding webs 34 have a lower thermalcross-section than the surrounding connection region, thus simplifyingthe process of attachment via welding or soldering.

The holding webs 34 are additionally designed so as to compensate fordifferent coefficients of expansion during operation (which involvesheating). This occurs because the holding webs 34 are suited forabsorbing mechanical stress loads. In the embodiment shown, thegeometrical arrangement is such that, for straight holding bars or webs34, a twisting of the contact pad 32 is possible. This is achievedthrough a broken symmetry when connecting the contact pad and theconnection region. Another possibility (not shown) is, e.g., to designthe holding webs in a meander or zig-zag shape.

The invention thus permits direct connection of a passive component to amultilayer printed circuit board structure without additional connectingmeans, cables, bond wires, etc. Only the actual connection (generally bymeans of soldering) of the component need be performed. The contactpaths are thus shortened, the number of solder connections decreased andreliability consequently increased, parasitic inductances are reduced,and integration density is increased.

We claim:
 1. An electronic assembly group comprising: a printed circuitboard structure with a multilayer structure having at least twoelectrically conductive layers; an additional passive component which isconnected to the two electrically conductive layers; wherein each of thetwo electrically conductive layers has at least one segment that extendsbeyond the multilayer structure to form connection regions, and thepassive component making contact directly at the connection regions. 2.The electronic assembly group according to claim 1, wherein themultilayer printed circuit board structure comprises at least oneelectrically conductive carrier layer having a semiconductor element andat least one further electrically conductive layer which is connected tothe semiconductor element.
 3. The electronic assembly group according toclaim 1, wherein the additional passive element is a capacitor or aninductor.
 4. The electronic assembly group) according to claim 3,wherein the capacitor is an annular capacitor surrounding the multilayerprinted circuit board structure.
 5. The electronic assembly groupaccording to claim 3, wherein a load inductor directly connected toconnection regions is provided.
 6. The electronic assembly groupaccording to claim 1, wherein the multilayer printed circuit boardstructure is connected to a heat sink.
 7. The electronic componentaccording to claim 5, wherein the load inductor is directly connected tothe heat sink.
 8. The electronic assembly group according to claim 1,the electronic assembly group is mounted or potted in a casting jacket.9. The electronic assembly group according to claim 1, wherein at leastone of the connection regions comprises at least one recess with acontact pad) contained therein for making contact with a passivecomponent.
 10. The electronic assembly group according to claim 9,wherein the contact pad is configured to make direct contact with theSchoop layer of a foil capacitor.
 11. The electronic assembly groupaccording to claim 9, wherein the contact pad is electrically connectedto the connection region by means of at least one holding web.
 12. Theelectronic assembly group according to claim 11, wherein the holding webis designed so as to compensate for any mechanical stress that occurswhen the assembly is in operation.
 13. An arrangement consisting of amultilayer printed circuit structure having at least one integratedpower semiconductor and an additional passive component, whereinconnection regions for the passive component are routed directly out ofthe multilayer printed circuit board structure and connected directly tothe passive component.
 14. An electric motor comprising: an electronicassembly group according to claim 1 designed as a rectifier/inverter,wherein in order to form a heat sink the multilayer printed circuitboard structure is directly mounted on a cooling region of the electricmotor.
 15. A method for producing an electronic assembly group, themethod comprising the following steps: providing a multilayer printedcircuit board structure comprising an electrically conductive carrierlayer and at least one further electrically conductive layer, the layershaving layer sections projecting beyond a core region of the multilayerstructure; removing at least partially layer sections projecting beyondthe core region (K) which are not needed as connection regions; removingat least partially prepreg layer sections projecting beyond the coreregion; forming connection regions on the remaining layer sectionsprojecting beyond the core region; and making direct contact between apassive element and the connection regions.
 16. The method according toclaim 15, wherein the step of forming the connection regions comprisesthe step of bending the remaining layer sections projecting beyond thecore region.
 17. The method according to claim 15, wherein prior to thestep of at least partially removing the layer sections projecting beyondthe core region which are not required as connection regions, thefollowing steps are performed: producing a through-contact between aprojecting layer section of the further electrically conductive layerand a projecting layer section of the carrier layer; and separating theprojecting layer section of the further electrically conductive layerfrom the further electrically conductive layer.
 18. The method accordingto claim 15, wherein the two steps of partially removing are carried outas follows: forming a bending region on either side of the core regionby performing limited removal of all layers, with the exception of theconnection regions, by means of deep milling.
 19. The method accordingto claim 15, wherein, following the steps of partially removing, anyremaining regions with layer sequences below the connection regions actas spacers with respect to a housing surrounding the electronic assemblygroup.
 20. The method according to claim 15, wherein separating meansfor mechanically removing the prepreg layer sections from the futureconnection regions are provided between the projecting layer sectionsand their adjacent prepreg layer sections.
 21. The method according toclaim 15, wherein the removal of the layer sections which are notrequired as a connection region is carried out by etching, and theremoval of the prepreg layer sections projecting beyond the core regionis carried out by milling.
 22. The method according to claim 15, whereinthe layer sections projecting beyond the core region which are notrequired as a connection region and the prepreg layer sectionsprojecting beyond the core region are substantially removed in full.